1. Field of the Invention
The present invention relates to a system and method for an antenna for a tire pressure monitoring device having reduced coupling to metal objects.
2. Background Art
It is known in the automotive industry to provide for wireless monitoring of vehicle tire parameters, particularly tire pressure. In such tire pressure monitoring systems, tire pressure sensors and radio frequency (RF) transmitters including antennas are mounted inside each tire, typically adjacent the inflation valve stem on or near a metal wheel rim. In each tire, the tire pressure sensed by the tire pressure sensor is transmitted as an RF signal by the transmitter through the antenna to a receiver/controller located on the vehicle. The tire pressure information delivered to the receiver/controller by the RF signals from the transmitters is subsequently conveyed to a vehicle operator or occupant, typically using a display unit. In such a fashion, tire pressure monitoring systems can help to improve vehicle safety. Exemplary tire pressure monitoring systems are described and shown in U.S. Pat. Nos. 6,112,587 and 6,034,597.
Remote keyless entry (RKE) systems are also well known in the automotive industry. RKE systems include an RF transmitter used by the vehicle operator or occupant to transmit signals that control such functions as door, trunk, etc. locking/unlocking, turning on/off lights, sounding an alert, arming/disarming an anti-theft system, etc. and a receiver/controller in the vehicle that processes the transmitter control signals. The conventional RKE receiver includes an RF antenna that is generally positioned or mounted on or near metal objects such as exterior body sheet metal, internal body structural metal, metal door skins, etc.
Conventional RF antennas that are mounted near metal objects (e.g., the tire pressure monitoring device antennas that are mounted on the vehicle wheel rims, the RKE antennas that are mounted on body sheet metal, etc.) are de-tuned from one application to the next because of metal coupling between active (i.e., radiating or receiving) antenna elements and the metal near the antenna.
Thus, there exits a need for a system and method for an antenna for a tire pressure monitoring wheel electronic device and RKE applications that, when mounted on or near metal such as the rim of the wheel or body sheet metal, reduces or eliminates the metal coupling between the antenna element and the metal. Such an antenna would reduce the de-tuning due to the metal coupling and improve the antenna efficiency and performance when compared to conventional RF antenna approaches.